Terbinafine has been known as an effective antifungal agent and used particularly in the treatment of tinea unguium. Tinea unguium is a difficult-to-treat disease that is caused by Trichophyton invasion into nails and characterized by symptoms such as opaque, thickened, and deformed nail surface. Tinea unguium is currently treated in most cases by means of the long-term oral administration of antifungal agents such as terbinafine or itraconazole. However, there are problems such as severe side effects such as liver damage, attributed to the long-term administration of the antifungal agents, and interaction with other agents.
By contrast, external preparations for nails, which have low drug permeation into blood, are thought to be able to reduce side effects attributed to the oral administration of antifungal agents. Some external preparations for nails comprising an antifungal agent have been proposed so far. However, these preparations do not provide the sufficient amount of the drug permeated into nails having high barrier functions. Therefore, they do not always have high therapeutic effects under present circumstances.
Such an external preparation for nails is, for example, a liquid medicine comprising an antifungal agent (Patent Document 1). However, for the liquid medicine, a dose to an affected part is difficult to adjust, and continued administration is also difficult. Therefore, it is thought that sufficient drug permeation into nails is not obtained. Moreover, a nail lacquer comprising an antifungal agent has also been proposed (Patent Document 2). This preparation permits continued administration. However, an administration method thereof is complicated. Additionally, it does not always have high drug permeability and, furthermore, might cause stained or discolored nails.
Furthermore, patches comprising an antifungal agent have also been proposed in terms of easy administration (Patent Documents 3 to 6). These nail patches provide more improved usability than those of external preparations other than patches, such as liquid medicines, and also permit long-lasting effects of the drug when directly attached to nails. Therefore, they have improved drug permeability into nails. However, the amount of the drug permeated sufficient for the treatment of tinea unguium still remains to be achieved.    Patent Document 1: Japanese Patent Laid-Open No. 2002-68975    Patent Document 2: Japanese Patent Laid-Open No. 5-85929    Patent Document 3: Japanese Patent Laid-Open No. 10-330247    Patent Document 4: National Publication of International Patent Application No. 2003-525641    Patent Document 5: National Publication of International Patent Application No. 1997-504536    Patent Document 6: National Publication of International Patent Application No. 2005-501885